The principal aims of the proposed research are (1) to provide dielectric property information on living neoplastic and normal tissues over the continuous frequency range of 0.0005 GHz (gigahertz) to 10.0 GHz using an in vivo probe measurement technique recently developed at Georgia Tech and (2) to determine if differences exist in the dielectric characteristics of living neoplastic and normal tissues. Considerable need exists for accurate determination of the in vivo dielectric properties of normal and neoplastic tissues. In vivo measurements performed over a wide frequency range (0.0005-10.0 GHz) and with minimum effect on the living system can aid considerably in the development of electromagnetically (EM) induced hyperthermia as a method for treating widely metastasizing diseases. By determining the dielectric properties of the diseased and normal tissue, it should be possible to identify frequencies at which EM hyperthermia would be most effective without damaging normal tissues. In the proposed study it is planned to (1) measure the in vivo dielectric properties of normal and neoplastic tissues in animals and surface tumors and normal skin tissue in humans, (2) identify differences in the dielectric properties of normal and neoplastic tissues, (3) perform initial studies of the possibility of using this probe measurement technique for disease diagnosis, and (4) evaluate illuminator designs used for EM hyperthermia.